Select a photo or group of photos, then go to the Photo menu in the operating system menu bar. Mouse over Open With and choose the editing application you wish to use.

Choose the File Options for the images you wish to edit, then click Continue.

Edit as desired with the selected application. When you’re finished, choose Save As or Export, give your edited photo a unique file name, and then save the edited image to the same folder as the Original. Mylio Photos will automatically see the new version and add it to your library.